Benzoxazine compounds have been employed satisfactorily to produce prepregs, laminates, moulding material, RTM (resin transfer moulding) systems, sealants, sinter powders, cast articles, structural composites parts, varnishes, surface coatings, electrical and electronic components by impregnating, coating, laminating or moulding processes. Such resins are dimension stable and have good electrical and mechanical resistance, low shrinkage, low water absorption, medium to high glass transition temperatures and good retaining properties, in term of mechanical properties.
Benzoxazine compounds can easily be produced in several, well known ways by the reaction of bisphenols with a primary amine and formaldehyde, whereby the process can be carried out in the presence of solvents (see for example U.S. Pat. Nos. 5,152,993 or 5,266,695) or in the absence of solvents (see for example U.S. Pat. No. 5,543,516). The common manufacture and various curing possibilities using hardeners such as novolacs, polyepoxides or polyamines optionally together with catalysts, or the catalytical and/or thermal curing as well as the valuable properties of the resins make this class of thermosetting resins attractive.
EP 0 149 987 A2 describes a thermosetting resin composition with improved storage stability comprising dihydrobenzoxazines of polyphenols and a reactive polyamine or polyamine generating compound. The composition is used for the manufacture of moulded, encapsulated articles or laminates, or of coatings. The composition is conveniently used as solution in organic solvents for surface coating applications. The solution with poly(dihydrobenzoxazines) and polyamines is stabilized by formation of an organic acid salt of the polyamines, whereby acids are selected from preferably volatile aliphatic mono carboxylic acids. The only disclosed purpose of an organic acid addition is the stabilization of the solution at about room temperature.